Ultrasound technology was proved as an efficient processing technique to obtain micro-molded specimens of polylactide (PLA) and polybutylene succinate (PBS), which were selected as examples of biodegradable polyesters widely employed in commodity and specialty applications. Operational parameters such as amplitude, molding force and processing time were successfully optimized to prepare samples with a decrease in the number average molecular weight lower than 6%. Ultrasonic waves also seemed an ideal energy source to provide effective disaggregation of clay silicate layers, and therefore exfoliated nanocomposites. X-ray diffraction patterns of nanocomposites prepared by direct micro-molding of PLA or PBS powder mixtures with natural montmorillonite or different organo-modified clays showed the disappearance of the 001 silicate reflection for specimens having up to 6 wt.% clay content. All electron micrographs revealed relatively homogeneous dispersion and sheet nanostructures oriented in the direction of the melt flow. Incorporation of clay particles during processing had practically no influence on PLA characteristics but enhanced PBS degradation when an organo-modifier was employed. This was in agreement with thermal stability data deduced from thermogravimetric analysis. Cold crystallization experiments directly performed on micro-molded PLA specimens pointed to a complex influence of clay particles reflected by the increase or decrease of the overall non-isothermal crystallization rate when compared to the neat polymer. In all cases, the addition of clay led to a clear decrease in the Avrami exponent. (C) 2014 Elsevier B.V. All rights reserved.

Ultrasound technology was proved as an efficient processing technique to obtain micro-molded specimens of polylactide (PLA) and polybutylene succinate (PBS), which were selected as examples of biodegradable polyesters widely employed in commodity and specialty applications. Operational parameters such as amplitude, molding force and processing time were successfully optimized to prepare samples with a decrease in the number average molecular weight lower than 6%. Ultrasonic waves also seemed an ideal energy source to provide effective disaggregation of clay silicate layers, and therefore exfoliated nanocomposites. X-ray diffraction patterns of nanocomposites prepared by direct micro-molding of PLA or PBS powder mixtures with natural montmorillonite or different organo-modified clays showed the disappearance of the 0 0 1 silicate reflection for specimens having up to 6 wt.% clay content. All electron micrographs revealed relatively homogeneous dispersion and sheet nanostructures oriented in the direction of the melt flow. Incorporation of clay particles during processing had practically no influence on PLA characteristics but enhanced PBS degradation when an organo-modifier was employed. This was in agreement with thermal stability data deduced from thermogravimetric analysis. Cold crystallization experiments directly performed on micro-molded PLA specimens pointed to a complex influence of clay particles reflected by the increase or decrease of the overall non-isothermal crystallization rate when compared to the neat polymer. In all cases, the addition of clay led to a clear decrease in the Avrami exponent.

Kinetics of isothermal and non-isothermal crystallization studies of a biodegradable monofilament suture constituted by polyglycolide hard blocks and soft segments derived from glycolide, epsilon-caprolactone and trimethylene carbonate have been undertaken by means of calorimetric methods. This segmented polymer was semicrystalline with melting and crystallization characteristics defined by the polyglycolide hard segments. The amorphous phase had a glass transition temperature highly influenced by thermal processing and the random microstructure of the soft segment. Melting process was complex due to the occurrence of lamellae with different degree of perfection. Equilibrium melting point, determined by the Hoffman-Weeks methodology, became slightly lower than reported for polyglycolide and segmented copolymers having a lower soft segment content.; A heterogeneous nucleation and a three-dimensional crystal growth were characteristic for isothermal crystallizations performed from the melt state, being the Avrami exponent very close to 3 for all experiments. Secondary nucleation constant was evaluated from the overall crystallization rates and by assuming the validity of Lauritzen-Hofmann approach. Results point out a maximum rate for a crystallization temperature of 131 degrees C and probably an underestimated nucleation constant.; Kinetic parameters for non-isothermal crystallization were deduced by Avrami, Ozawa and Caze methods. A good agreement with isothermal parameters was only attained with the last methodology, although results from the other ones were appropriate to simulate the crystallization process. lsoconversional analysis was a good methodology to estimate the secondary nucleation constant from a non-isothermal crystallization. (C) 2014 Elsevier B.V. All rights reserved.

The synthesis of a series of poly(ester amide)s constituted by glycolic acid, adipic acid, and different ratios of 1,3-pentanediamine and 1,5-pentanediamine units was studied and the derived copolymers were characterized. Thermal polycondensation between the potassium adipate salt and the appropriate ratio of N,N-bis(chloroacetyl)-1,3-pentanediamine and N,N-bis(chloroacetyl)-1,5-pentanediamine was proved to be effective, proceeded with high yield, and rendered samples with moderate molecular weight for carefully controlled competitive thermal degradation reactions. Physical properties were highly dependent on the final composition. In particular, crystallinity and thermal stability decreased with 1,3-pentanediamine unit content, that is, with the incorporation of lateral ethyl groups into the main chain. The presence of these units also changed solubility in solvents like methanol and degradability in a protease K enzymatic medium. Specifically, incorporation of 1,3-pentanediamine units led to a gradual increase in degradability. All poly(ester amide)s were able to establish intermolecular hydrogen bonding interactions, which in semicrystalline samples pointed to typical sheet structures of polyamides according to X-ray diffraction and infrared spectroscopic data. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40102.

The synthesis of a series of poly(ester amide)s constituted by glycolic acid, adipic acid, and different ratios of 1,3-pentanediamine and 1,5-pentanediamine units was studied and the derived copolymers were characterized. Thermal polycondensation between the potassium adipate salt and the appropriate ratio of N,N-bis(chloroacetyl)-1,3-pentanediamine and N,N-bis(chloroacetyl)-1,5-pentanediamine was proved to be effective, proceeded with high yield, and rendered samples with moderate molecular weight for carefully controlled competitive thermal degradation reactions. Physical properties were highly dependent on the final composition. In particular, crystallinity and thermal stability decreased with 1,3-pentanediamine unit content, that is, with the incorporation of lateral ethyl groups into the main chain. The presence of these units also changed solubility in solvents like methanol and degradability in a protease K enzymatic medium. Specifically, incorporation of 1,3-pentanediamine units led to a gradual increase in degradability. All poly(ester amide)s were able to establish intermolecular hydrogen bonding interactions, which in semicrystalline samples pointed to typical sheet structures of polyamides according to X-ray diffraction and infrared spectroscopic data.

Poly(butylene azelate-co-butylene succinate) samples with different azelate/succinate ratios were synthesized and characterized. Calorimetric data indicate a semicrystalline character for all copolyesters studied and a melting point depression that could be interpreted on the basis of complete exclusion of comonomers from well organized lamellae. Crystallization first occurred through the succinate rich segments, which resulted in a peculiar behavior of copolymers having an intermediate composition. In this case, crystallization of azelate segments was paradoxically enhanced when samples were quenched. Equilibrium melting temperatures significantly decreased with increasing comonomer content compared to those of the corresponding homopolymers. Incorporation of comonomers had a distinct effect on the secondary nucleation constant depending on the composition as deduced from Lauritzen and Hoffman analysis. Thus, azelate units clearly increased the nucleation constant of copolymers rich on succinate units, whereas the incorporation of succinate units had a lower influence on the constant of copolyesters having high azelate content.

Poly(butylene azelate-co-butylene succinate) samples with different azelate/succinate ratios were synthesized and characterized. Calorimetric data indicate a semicrystalline character for all copolyesters studied and a melting point depression that could be interpreted on the basis of complete exclusion of comonomers from well organized lamellae. Crystallization first occurred through the succinate rich segments, which resulted in a peculiar behavior of copolymers having an intermediate composition. In this case, crystallization of azelate segments was paradoxically enhanced when samples were quenched. Equilibrium melting temperatures significantly decreased with increasing comonomer content compared to those of the corresponding homopolymers. Incorporation of comonomers had a distinct effect on the secondary nucleation constant depending on the composition as deduced from Lauritzen and Hoffman analysis. Thus, azelate units clearly increased the nucleation constant of copolymers rich on succinate units, whereas the incorporation of succinate units had a lower influence on the constant of copolyesters having high azelate content

Random copolymers derived from 1,4-butanediol and two dicarboxylic units differing in the parity of the number of methylene groups and length of the polymethylene sequence (i.e. succinic and azelaic acids) were studied in terms of thermal properties, crystalline structure and morphology, crystallization kinetics and biodegradability.
All samples were semicrystalline and their thermal properties varied in a wide temperature range. Copolymers crystallized according to the monoclinic α-form of polybutylene succinate and the orthorhombic structure postulated for polybutylene azelate depending on the predominant dicarboxylate unit. The behavior of the copolymer with an intermediate composition was complex due to strong dependence of the predominant crystalline form on crystallization and processing conditions. Interestingly, crystallization into the azelate structure was favored when samples were rapidly cooled from the melt, resulting in an unexpected increase in the degree of crystallinity. Spherulitic morphologies were clearly different (i.e. ringed spherulites and axialites) depending on the preferential crystalline structure.
Enzymatic degradability of the two homopolyesters was highly different and could be enhanced by incorporation of comonomer units. Preferential enzymatic attack on amorphous regions highlighted the spherulitic morphologies of copolymers having well developed, distinctive ringed structures.

Basic diffraction data on nylon 47 pointed out a peculiar structure of hydrogen bonds along
two directions. Nylon 47 showed reversible polymorphic transitions during heating/cooling
processes that were analyzed by real time synchrotron WAXD experiments. Results
indicated that nylon 47 had a first structural transition at low temperature, followed by
a gradual Brill transition towards a pseudohexagonal packing.
Nylon 47 crystallized from the melt giving rise to spherulites with different characteristics
than those attained with conventional even-even nylons. Interestingly, spherulites
crystallized at low supercooling underwent a reversible change in birefringence with temperature.
This was due to the reversible structural changes caused by temperature variations
and the flat on lamellar morphology.
Intercalated and exfoliated nanocomposites based on nylon 47 were prepared by solution
intercalation and melt mixing using Cloisites 25A and 30B. The influence of the final
silicate layer morphology on the hot crystallization behavior was investigated. Crystallization
rates of the neat polymer and its two nanocomposites were significantly different,
mainly due to variations in the primary nucleation

Hydrolytic degradation of a series of copolymers synthesized by ring opening polymerization of trimethylene carbonate and glycolide was studied by following the weight loss and changes in molecular weight, polydispersity index and mechanical properties. Analyses of H-1 NMR and FTIR spectra taken during exposure to a pH 7.4 phosphate buffered solution were also performed. Copolymers with different microstructures (i.e. random, triblock and segmented copolymers) were synthesized. Most segmented copolymers studied had identical trimethylene carbonate content but differed in the hard segment content. Composition was also varied to demonstrate the influence of the soft segment composition.
Results were consistent with a model where degradation started in the amorphous phases and affected the glycolide units of the less compact soft segments and the regions within lamellar stacks. This degradation step led to a clear decrease of GGG triads (NMR data) and amorphous glycolide content (FTIR data), as well as an increase in Young's modulus. Degradation subsequently proceeded through the crystalline glycolide units belonging to lamellar stacks. The molecular weight of the degraded samples reached always an asymptotic value that corresponded to a solubility limit for fragments with high TMC content and for highly crystalline entities constituted by glycolide rich fragments.
Results pointed to the importance of the hard segment content and the composition of the soft segment, which logically influenced the distribution between amorphous and crystalline phases.

The thermal stability and degradation kinetics of poly(trimethylene carbonate) (PTMC) blends with different ratios of polylactide (PLA) and alternatively polycaprolactone (PCL) were investigated by thermogravimetric analysis under a nitrogen atmosphere. These studies were extended to the single components (i.e. PCL and PLA). In all cases, the derivative thermogravimetric curves indicated a complex decomposition process with at least two degradation steps. The kinetic parameters of the main step, including activation energy, reaction model and pre-exponential factor, were evaluated by the Kissinger, isoconversional (Friedman and KAS) and Coats–Redfern methods. Data of the main decomposition process were obtained by mathematical deconvolution of experimental DTG curves acquired at heating rates ranging from 2 to 40 °C/min.
It was demonstrated that degradation of blends did not correspond to a mere superposition of the characteristic decomposition processes of the two involved polymers. Furthermore, PCL and PLA influenced the decomposition of the less thermally stable PTMC component in a different way. Thus, PLA modified the degradation of PTMC, and specifically led to thermal stabilization and a new decomposition process characterized by a higher activation energy. On the other hand, PCL favored the degradation of PTMC by enhancing a typical minor decomposition process that occurred in the single component at a lower temperature.
The main decomposition step of PTMC, PLA, PCL and the studied blends always followed an Avrami model but with significant differences in their exponents (i.e. from 2 to 7

The thermal stability and degradation kinetics of poly(trimethylene carbonate) (PTMC) blends with different ratios of polylactide (PLA) and alternatively polycaprolactone (PCL) were investigated by thermogravimetric analysis under a nitrogen atmosphere. These studies were extended to the single components (i.e. PCL and PLA). In all cases, the derivative thermogravimetric curves indicated a complex decomposition process with at least two degradation steps. The kinetic parameters of the main step, including activation energy, reaction model and pre-exponential factor, were evaluated by the Kissinger, isoconversional (Friedman and KAS) and Coats–Redfern methods. Data of the main decomposition process were obtained by mathematical deconvolution of experimental DTG curves acquired at heating rates ranging from 2 to 40 °C/min.
It was demonstrated that degradation of blends did not correspond to a mere superposition of the characteristic decomposition processes of the two involved polymers. Furthermore, PCL and PLA influenced the decomposition of the less thermally stable PTMC component in a different way. Thus, PLA modified the degradation of PTMC, and specifically led to thermal stabilization and a new decomposition process characterized by a higher activation energy. On the other hand, PCL favored the degradation of PTMC by enhancing a typical minor decomposition process that occurred in the single component at a lower temperature.
The main decomposition step of PTMC, PLA, PCL and the studied blends always followed an Avrami model but with significant differences in their exponents (i.e. from 2 to 7).

Polymer clay nanocomposites of polyamides and biodegradable polymers with three kinds of organomodified clays were prepared by different techniques (in situ polymerization, solution casting, and melt mixing). The polymers used in this
research were nylons 56, 65 and 47 and the biodegradable polymers: poly (glycolic acid-alt-6-hydrohexanoic acid) and
poly(glycolic acid-alt-6-aminohexanoic acid). The development of biodegradable nanocomposites with improved or modified material properties is an interesting topic since these new materials are expected to replace already existing biodegradable
and non-biodegradable commodity plastics in some specific applications.This project aims to study the influence of clay particles incorporated in a polymer matrix on the crystallization processes, the study of the in situ polymerization kinetics of
mixtures of clays and monomers of biodegradable polymers, as well as the influence of nanoparticles on the thermal behavior and morphologic parameters.
Even-odd, and odd-even polyamides were chosen to study the Brill transition and to prepare nanocomposites with organomodified clays. These polyamides have a peculiar structure where hydrogen bonds are established along two
different directions. X-ray diffraction as well as SAXS-WAXD synchrotron experiments were employed to study the structural changes induced by temperature, during heating and cooling. Different organomodified clays were used to prepare nanocomposites, which final structure was found to be dependent on the preparation method.
Nanocomposites derived from biodegradable polymers were characterized by means of X-ray diffraction and transmission electron microscopy. Morphological studies showed that the extent of clay dispersion depended on the clay type and on the preparation technique. Hence, exfoliated and intercalated nanocomposites could be obtained. The final nanocomposite structure was found to have a great influence on both cold and hot crystallization processes. Hence, the crystallization rate increased and decreased with respect to the neat polymer when intercalated and exfoliated structures were respectively obtained. The kinetics of the polymerization process was also studied by means of FTIR and SAXS-WAXD. The results
indicate that the presence of the organomodified clay had a remarkable effect on the kinetic parameters.

The non-isothermal degradation kinetics of poly(trimethylene carbonate) (PTMC) and polyglycolide (PGL) was investigated by thermogravimetric (TG and DTG) analysis in the temperature range between 50 and 550 °C at different heating rates (0.5–40 °C/min). Both homopolymers showed a complex multi-step degradation process. Kinetic analysis was successfully performed for the main degradation steps using the isoconversional Kissinger–Akahira–Sunose and Friedman methods. Activation energies of these steps were practically independent of the degree of conversion. The true kinetic triplets (E, A, f(α)) were determined by the Coats–Redfern method. The results clearly indicated that the two homopolymers mainly degraded by quite different mechanisms, i.e. A3 and F1, which may be associated with different depolymerization processes (e.g. decarboxylation or unzipping).
Degradation of copolymers of trimethylene carbonate and glycolide with different chemical microstructures (i.e. random, blocky and segmented) and of blends with different percentages of both homopolymers was also studied. Interestingly, a deceleration and an acceleration for the decomposition of trimethylene carbonate and glycolide segments were observed, respectively. Specifically, the two-step degradation process of the blend with 50 wt% of each homopolymer was analyzed by the above methodologies. Kinetic data indicated that the main degradation process involved a different mechanism from that previously determined for PTMC and PGL, and that the activation energy was intermediate (i.e. EPTMC < EBlend < EPGL).

Copolymers of glycolide and trimethylene carbonate with different compositions and microstructures (i.e. random, blocky and segmented) were synthesized by two-step ring opening polymerization.
NMR analyses revealed that transesterification reactions took place during the first step, which corresponded to the synthesis of soft segments, and mainly when the trimethylene carbonate content of the reaction medium was high. The transesterification percentage did not significantly change with the addition of hard blocks in the second reaction step. Infrared spectroscopy was a complementary, highly effective tool to evaluate the hard segment length, crystallinity and glycolide percentage incorporated into the crystalline phase for all studied samples.
Calorimetric analyses showed dependency of properties on the length of the polyglycolide hard segment and also good miscibility between glycolide and trimethylene carbonate rich phases. Crystalline morphologies attained with segmented and random copolymers were significantly different, although in all cases a positive birefringence was detected.
Thermogravimetric analyses indicated that all studied copolymers had a similar degradation behavior, which was intermediate between those observed in the corresponding homopolymers. Samples with a significant glycolide unit content showed a stabilizing effect for the degradation of poly(trimethylene carbonate) blocks.

Scaffolds of a biodegradable poly(ester amide)constituted of L-alanine, sebacic acid, and 1,12-dodecanediol units (abbreviated as PADAS) were prepared by the
compression-molding/particulate-leaching method. The influence of the type, size, and percentage of salt on the scaffold porosity and morphology was evaluated. The thermal
behavior and crystallinity were also studied for samples obtained under different processing conditions.
PADAS scaffolds were not cytotoxic because they showed good cell viability and supported cell growth at a similar ratio to that observed for the biocompatible materials used as a reference. The use of PADAS scaffolds as a drug-delivery system was also evaluated by the employment of ibuprofen, a drug with well known anti-inflammatory effects. Different drug-loading methods were considered, and their influence on the release in a so¨rensen’s medium was evaluated as well as the influence of the scaffold morphology.
A sustained release of ibuprofen could be attained without the production of a negative effect on the cell viability. The
release kinetics of samples loaded before melt processing was well described by the combined Higuchi/first-order model. This allowed the estimation of the diffusion coefficients, which ranged between 3x10‾14 and 5x10‾13 m2/ s. Samples loaded by immersion in ibuprofen solutions showed a rapid release that could be delayed by the addition of polycaprolactone to the immersion medium (i.e., the release rate decreased from 0.027 to 0.015 h‾1).

An intercalated nanocomposite of the organically modified montmorillonite Cloisite C25A and a degradable
poly(ester amide) based on glycolic acid and 6-aminohexanoic acid units (poly(glc-alt-amh)) was
prepared using a twin-screw co-rotating extruder. The non-isothermal degradation kinetics was investigated
by thermogravimetric analysis (TG and DTG) in the temperature range of 50–600 ◦C at five
heating rates (2, 5, 10, 20 and 40 ◦C/min) and compared with the neat polymer. Significant differences
were found since the nanocomposite showed three degradation steps instead of the two decomposition
processes detected in the pristine sample. The onset mass loss temperature decreased in the
nanocomposite due to the presence of the organo-modifier compound, but the presence of the silicate
layers significantly decreased the degradation rate at the last stages of decomposition. Kinetic analysis
was performed using the Kissinger method and the isoconversional (Kissinger–Akahira–Sunose
and Friedman) methods. The true kinetic triplets (E, A, f(˛)) were determined for the first two
steps of degradation through the Coats–Redfern and the Invariant Kinetic Parameters methods. The
results clearly indicated that the presence of the organo-modified clay modified the mechanisms of
degradation.

Poly(ester amide)s are an emerging group of biodegradable polymers that may cover both commodity and speciality applications. These polymers have ester and amide groups on their chemical structure which are of a degradable character and provide good thermal and mechanical properties. In this sense, the strong hydrogen‑bonding interactions between amide groups may counter some typical weaknesses of aliphatic polyesters like for example poly(e-caprolactone). Poly(ester amide)s can be prepared from different monomers and following different synthetic methodologies which lead to polymers with random, blocky and ordered microstructures. Properties like hydrophilic/hydrophobic ratio and biodegradability can easily be tuned. During the last decade a great effort has been made to get functionalized poly(ester amide)s by incorporation of a-amino acids with hydroxyl, carboxyl and amine pendant groups and also by incorporation of carbon-carbon double bonds in both the polymer main chain and the side groups. Specific applications of these materials in the biomedical field are just being developed and are reviewed in this work (e.g., controlled drug delivery systems, hydrogels, tissue engineering and other uses like adhesives and smart materials) together with the main families of functionalized poly(ester amide)s that have been developed to date.

The influence of degradation on non-isothermal crystallization from the melt of a segmented copolymer
constituted of glycolide and trimethylene carbonate units and used as a bioabsorbable surgical suture
was studied by optical microscopy, differential scanning calorimetry and time-resolved X-ray diffraction.
Fibrillar positive spherulites were obtained with slightly degraded samples but new axialitic morphologies
were detected when samples had a molecular weight, Mw, lower than 29,000 g/mol and the
crystallization started at a high temperature.
Crystal growth kinetics of samples degraded under different conditions was evaluated over a wide
temperature range by a non-isothermal method. Two crystallization regimes (I and II) were determined
for the more degraded samples (i.e., those able to crystallize according to axialitic and spherulitic
morphologies), whereas only regime II was found for samples of higher molecular weights. Primary
nucleation density decreased with the extent of degradation provided no morphological changes
occurred, and so did the regularity of lamellar stacking, as shown by synchrotron measurements,
although the morphological parameters remained practically constant.

Brill transition and crystallization behaviour of nylon 56, a representative polymer of odd–even polyamides, were investigated by simultaneous WAXD and SAXS synchrotron radiation. Nylon 56 crystallized from solution into a peculiar structure where hydrogen bonds were established along the two directions. Nylon 56 experimented on heating a Brill transition that lead to a pseudohexagonal packing and lately to a monoclinic unit cell where neighbouring molecular segments were shifted along the chain axis direction. In disagreement with conventional polyamides, the Brill transition of nylon 56 was not reversible since on cooling the pseudohexagonal arrangement was mainly attained. Optical microscopy studies performed under both isothermal and non-isothermal conditions demonstrated that nylon 56 spherulites had different optical properties than even–even nylons having conventional sheet structures. The birefringence sign changed in the sequence positive–negative–positive when crystallization temperature was decreased.

The isothermal crystallization behavior of a segmented copolymer constituted by hard blocks of polyglycolide and soft segments derived from the copolymerization of glycolide and trimethylene carbonate was investigated. This polymer has applied relevance because it is one of the most widely used for bioabsorbable surgical sutures. Calorimetric, optical microscopy, and infrared techniques were combined to understand the thermal properties and the different factors that influence the crystallization process. Basically, only the hard blocks crystallized, although certain processing conditions allowed performing an additional crystallization associated with small lamellar domains of the soft segment. Crystallization from both the melt and the glass state rendered positive spherulites with a fibrillar texture. The observed unusual sign of birefringence was a consequence of the close packing structure of polyglycolide, which was also corroborated by electron diffraction patterns. Crystallization was characterized by an athermal nucleation, which allowed accurate estimation of the secondary nucleation parameter by using the calorimetric data only. Significant differences in the Avrami exponent (from 2.32 to 1.45) were found between the cold and hot isothermal crystallizations. The stronger geometric constraints observed in the crystallization from the glass state were also corroborated by FTIR analyses